A containment system and a method for using said containment system

ABSTRACT

A containment system for recovering hydrocarbon fluid from a leaking device comprising a dome sealed to the seafloor around the leaking device and forming a cavity for accumulating hydrocarbon fluid. The dome comprises a first dome and a second dome connected to the first dome. The second volume of the second dome is smaller than the first volume of the first dome.

RELATED APPLICATIONS

The present application is a National Phase entry of PCT Application No. PCT/IB2014/000569, filed Mar. 7, 2014, which claims priority from EP Patent Application No. 13306446.9, filed Oct. 21, 2013, said applications being hereby incorporated by reference herein in their entirety.

FIELD OF THE INVENTION

The present invention concerns a containment system for recovering spilled oil that is leaking under water.

BACKGROUND OF THE INVENTION

The present invention concerns more precisely a containment system for recovering a hydrocarbon fluid from a leaking device that is situated at the seafloor and that is leaking the hydrocarbon fluid from a well.

Recovering oil that is leaking from an under water oil device is a great problem, especially for oil device that are installed at deep sea floor.

The explosion on the “Deepwater Horizon” platform in the Gulf of Mexico demonstrated how much such a containment system is difficult to control.

One of the main problems was the formation of hydrates that clogged the used containment system.

For example, at a depth of around 1500 meters, the sea water is cold (for example around only 5° C.) and at a high pressure. These environment conditions may transform the sea water and hydrocarbon fluid into hydrates having a quasi-solid phase and which can fill and clogged any cavity.

Hydrates inhibitors like methanol could be injected to avoid hydrate formation. But, the needed quantity of such chemical is huge and inhibitors are also pollution for the environment.

Heating of the containment system could be used to avoid hydrate formation. But, as the volume of cavity of the containment system is great, the heating is slow and amount of heat is too important.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a containment system that avoids the formation of hydrates inside the dome. More specifically, the aim of the invention is to provide a containment system having a large cavity volume, but that needs a reduced quantity of inhibitors or a reduced amount of heat to avoid hydrates formation and clogging of the containment system.

To this effect, the containment system of present invention is adapted to be landed at the seafloor corresponding to a base level of the containment system. It comprises:

-   -   a dome intended to be secured to the seafloor around the leaking         device and forming a cavity under said dome, said cavity being         adapted to completely surround and include the leaking device,         and to accumulate hydrocarbon fluid coming upwardly from the         leaking device, said dome comprising at least one upper output         opening adapted to extract the hydrocarbon fluid for recovering,         and     -   an anti hydrates system that actively prevents or remediates         hydrates inside the cavity.

The dome of the invention is composed at least of a first dome having a first volume adapted to receive the leaking device, and a second dome having a second volume smaller than the first volume, the second dome being situated upper to the first dome, and the first and second volumes being in communication via a dome opening.

Thanks to these features, the second volume can be more easily controlled for preventing or remediating hydrates formation. The containment system can be installed more easily without the annoying hydrates.

The anti hydrates system may be an injection system that injects injection fluid inside the cavity for preventing or remediating hydrates formation. Then, the second volume can be filled with the injection fluid, and hydrates formation can be prevented inside said second volume.

The quantity of injection fluid is reduced compared to the quantity that would be needed to avoid hydrates formation inside the volume of the first dome.

The anti hydrates system may be a heating system that heats at least a portion of the cavity, and more particularly the second volume. Then, the second volume is heated to a temperature so as hydrates formation can be prevented inside said second volume.

Therefore, the hydrocarbon fluid can be extracted from the second volume by the output opening situated on the upper portion of the second dome.

In various embodiments of the containment system, one and/or other of the following features may optionally be incorporated.

According to an aspect of the containment system, the second volume is smaller than a ¼^(th) of the first volume, and preferably smaller than a 1/10^(th) of the first volume.

According to an aspect of the containment system, the second volume is higher than a 1/20^(th) of the first volume.

According to an aspect of the containment system, the dome opening is between 2 and 4 meters wide.

According to an aspect of the containment system, the first dome is thermally insulated with an insulating material for having an overall heat transfer coefficient of the first dome lower than 1 W.m⁻².K⁻¹.

According to an aspect of the containment system, the anti hydrates system is only situated into or onto the second dome.

According to an aspect of the containment system, the anti hydrates system is a heating system for heating at least a portion of the cavity.

According to an aspect of the containment system, the anti hydrates system is an injection systems that inputs an injection fluid into the cavity.

According to an aspect of the containment system, the injection system comprises a plurality of output ports spread only inside the second volume or at the dome opening, said output ports being fed with the injection fluid.

According to an aspect of the containment system, the containment system further comprises a fluid heater for heating the injection fluid before injection into the cavity.

According to an aspect of the containment system, the injection fluid comprises one or a combination of the fluid components chosen in the list of water, salted water, dead oil, an alcohol, an ethanol, a methanol, a glycol, an ethylene glycol, a diethylene glycol, and a low-dosage hydrate inhibitor (LDHI).

According to an aspect of the containment system, the containment system further comprises a pipe having an inner tube forming an inner channel, and an outer tube surrounding said inner tube and forming an annular channel, and wherein the inner channel is used to extract the hydrocarbon fluid from the upper output opening and the annular channel is used to feed the injection system with at least an injection fluid, or inversely.

Another object of the invention is to provide a method for using a containment system for recovering hydrocarbon fluid from a leaking device that is situated at the seafloor and that is leaking hydrocarbon fluid from a well. The containment system comprises at least:

-   -   a dome forming a cavity under said dome to accumulate         hydrocarbon fluid coming upwardly from the leaking device, said         dome comprising at least one upper output opening adapted to         extract the hydrocarbon fluid for recovering, and     -   an anti hydrate system that actively prevents or remediates         hydrates inside the cavity, and     -   the dome comprises a first dome having a first volume, and a         second dome having a second volume smaller than the first         volume, the second dome being situated upper or above the first         dome.

The method of the invention comprises the following successive steps:

-   -   a) installing the first dome (20 ₁) on the seafloor around the         leaking device, the cavity completely surrounding and including         the leaking device,     -   b) installing the second dome (20 ₂) upper the first dome (20 ₁)         so as the first and second volumes are in communication via a         dome opening (26).

Thanks to the above method, the dome can be installed above the leaking device without hydrates formation inside the cavity, and the quantity of injection fluid is lower.

In preferred embodiments of the method proposed by the invention, one and/or the other of the following features may optionally be incorporated.

According to an aspect of the method, the anti hydrates system is a heating system for heating at least a portion of the cavity.

According to an aspect of the method, the anti hydrates system is an injection systems that inputs an injection fluid into the cavity.

According to an aspect of the method, the injection system injects the injection fluid into the second volume of the second dome before step b).

According to an aspect of the method, the containment system further comprises a level sensor and an output valve connected to the upper output opening, and the method further comprises after step b) the following steps:

-   -   c) measuring by the level sensor an interface level of a fluid         interface between hydrocarbon fluid and any other fluid inside         the dome,     -   d) controlling the output valve on the bases of the interface         level measured by the level sensor for outputting hydrocarbon         fluid from the cavity.

According to an aspect of the method, the injection system injects the injection fluid at a velocity that is low, and preferably at a velocity that is lower than 0.5 meter per seconds.

According to an aspect of the method, at step d), the output valve is controlled so as to keep the interface level lower or equal to a level of output of the hydrocarbon fluid from the leaking device.

BRIEF DESCRIPTION OF THE DRAWINGS

Other features and advantages of the invention will be apparent from the following detailed description of at least one of its embodiments given by way of non-limiting example, with reference to the accompanying drawings. In the drawings:

FIG. 1 is a schematic view of a vertical cut of a containment system according to a first embodiment of the invention;

FIG. 2 is a schematic view of a vertical cut of a containment system according to a second embodiment of the invention;

FIGS. 3a to 3e are an exemplary of a containment system according to the schematic of FIG. 1, showing a method for using or installing a containment system according to the invention;

FIG. 4 is a schematic view of a vertical cut of a containment system according to the invention incorporating a separation and mixing function, and

FIG. 5 is a schematic view of a vertical cut of a containment system incorporating a separation and mixing function.

In the various Figures, the same reference numbers indicate identical or similar elements. The direction Z is a vertical direction. A direction X or Y is a horizontal or lateral direction. These are indications for the understanding of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 is a first embodiment of a containment system 1 according to the invention. This containment system 1 is adapted for recovering hydrocarbon fluid from a leaking device 2 that is situated at a seafloor 5 of a deep offshore installation. The leaking device 2 is for example the well itself, a pipeline, a blow out preventer device, a wellhead or any device connected to the wellhead. The leaking device 2 is therefore usually a large device. It may be larger than 5 m. The seafloor 5 is for example at more than 1500 meters deep below the sea surface 4. At this depth, the sea water is cold, for example around only 5° C. and at high pressure.

The hydrocarbon fluid may be liquid oil, natural gas, or a mix of them.

The leaking device 2 is leaking a hydrocarbon fluid from an undersea well 3. The hydrocarbon fluid exiting from the undersea may be rather hot, for example above 50° C. However, the environment cold temperature and high pressure may transform the sea water and hydrocarbon fluid into hydrates having a quasi-solid or solid phase. These hydrates can fill and clogged any cavity.

The containment system 1 of present invention is landed and fixed to the seafloor by any means, such as anchoring or heavy weights 29 for compensating the upward Archimedes force applied on the containment system 1 by the hydrocarbon fluid that is lighter than the sea water (lower mass density). The seafloor corresponds in the present description to a base level of the containment system 1. The other levels are defined going upwards, in the vertical direction Z towards the sea surface 4.

The containment system 1 of present invention comprises at least:

-   -   a dome 20 intended to be secured to the seafloor around the         leaking device 2 and forming a cavity 21 under said dome 20,         said cavity being adapted to completely surround and include the         leaking device, and to accumulate the hydrocarbon fluid coming         upwardly from the leaking device, said dome comprising at least         one upper output opening 22 to extract the hydrocarbon fluid for         recovering, and     -   an anti hydrates system 30 that actively prevents or remediates         hydrates inside the cavity.

The term “actively” means that the anti hydrates system 30 inputs some amount of energy inside the cavity to prevent the hydrates. The added energy may be of any type. It may be a chemical energy and/or a thermal energy. The anti hydrates system 30 is not a “passive” device, just thermally insulating the dome or doing a gravity separation of the components in the fluid inside the dome.

The dome 20 is preferably fixed and/or sealed to the seafloor.

For example, the dome 20 comprises foot 20 c having heavy weights for sealing and securing the dome 20 to the seafloor.

The dome 20 completely surrounds the leaking device 2. In a horizontal plane (XY), the dome 20 has a closed loop shape encompassing the leaking device 2. Said shape may be for example a circle shape, a square shape or any polygonal shape.

The dome 20 has a diameter D20. This outer diameter corresponds to a maximum distance between two internal points of the dome, taken in a horizontal plane at a level near the base level BL. The diameter D20 is for example of 6 meters or more.

The dome 20 is higher than a total height of the leaking device 2. It has a height H20 of approximately 3 meters or more. It completely includes the leaking device 2 (i.e. the part above the base level. All that is under the seafloor is not taken into account as the dome is sealed to the seafloor).

The dome 20 defines an inner dome volume, called the cavity 21. This volume is isolated (not in communication) with the environment sea water. The thermal exchange between the cold sea water and the hydrocarbon fluid is cancelled. This first effect reduces the hydrate formation.

The dome 20 is a hollow structure.

The dome 20 according to the invention comprises at least two parts:

-   -   a first dome (20 ₁) having a first volume for receiving the         leaking device, and     -   a second dome (20 ₂) having a second volume smaller than the         first volume, said second dome being situated upper the first         dome (20 ₁), and the first and second volumes being in         communication via a dome opening 26.

The term “dome” means here a general enclosure or container having a downwardly opened portion so as to be positioned above and to enclose a member. The dome has a lateral portion (like a vertical cylinder) that extends vertically from a base level to an upper level and an upper portion (like a cap) that extends horizontally from the upper end of the lateral portion so as to close the upper portion. The dome has an inner cavity with a volume adapted to receive the member. The lateral portion and/or upper portion may have some holes adapted for specific purposes (fluid exchange between the inner volume and the outside of the dome).

The second volume may be smaller than one fourth (¼^(th)) of the first volume. Preferably, the second volume is smaller than one fifth (⅕^(th)) of the first volume. Preferably, the second volume is smaller than one tenth ( 1/10^(th)) of the first volume.

The second volume is therefore much smaller than the first volume, and hydrates formation can be more easily prevented inside the second volume than in the first volume.

The second volume is not null. Preferably, the second volume is higher than one thirtieth ( 1/30^(th)) of the first volume, and more preferably the second volume is higher than one twentieth ( 1/20^(th)) of the first volume.

The second volume corresponds to a buffer volume comprised between 3 minutes and 10 minutes of hydrocarbon fluids, when the flow of hydrocarbon fluids from the leaking device 2 is taken into account. Preferably, the second volume corresponds to a buffer volume higher than 5 minutes of the flow of hydrocarbon fluids from the leaking device 2.

In comparison, the first volume of the first dome 20 ₁ corresponds to between 30 minutes to 60 minutes (or more) of the flow of hydrocarbon fluids from the leaking device 2.

For example (first example):

-   -   the leaking device 2 may extend 6 meters in all directions;     -   the fist dome 20 ₁ may be 7 meters in all directions, having a         first volume of approximately 350 m³;     -   the dome opening is between 2 and 4 meters wide (preferably         between 3 and 4 meters wide); and     -   the second dome 20 ₂ may be less than 4 meters wide in all         directions, or less than 3 meters in all directions, or having a         second volume lower than 50 m³.

For example (second example), the leaking device is bigger (e.g. when it is a Christmas tree having a blowout preventer):

-   -   the leaking device 2 may extend 9 meters in all directions;     -   the first dome 20 ₁ may be 10 meters in all directions,         corresponding to a huge first volume of 1000 m³.

The other features may be similar or identical to first example.

The first dome 20 ₁ is landed on the seafloor and contains the leaking device 2. It is a hollow structure having:

-   -   an upper portion 24 extending in a radial direction to an outer         peripheral end 24 a, said radial direction being perpendicular         to the vertical direction AX (equal to direction Z on the         Figure), and     -   a lateral portion 25 extending from the upper portion 24         downwardly between an upper end 25 a and a lower end 25 b, said         lower end 25 b comprising for example the foot 20 c.

The lateral portion 25 has said diameter D20. Its inner diameter is wider than a total wide of the leaking device 2. For example, the inner diameter is of 6 meters or more.

The lateral portion 25 of the first dome is downwardly opened so as to surround the leaking device 2.

The upper portion 24 of the first dome 20 ₁ comprises the dome opening 26 having of small diameter compared to the dome diameter. The upper portion 24 and/or the dome opening 26 are adapted to be connected to the second dome 20 ₂. The dome opening 26 has for example a diameter of 3 meters or less.

The second dome 20 ₂ is secured to the upper portion 24 of the first dome 20 ₁. It is a hollow structure having a similar general shape as the first dome, i.e. having:

-   -   an upper portion, and     -   a lateral portion extending from the upper portion downwardly         between an upper end and a lower end.

The lateral portion of the second dome 20 ₂ has a diameter wider than the dome opening 26. For example, the diameter of the lateral portion is higher than 3 meters, and preferably lower than 5 meters.

The second dome 20 ₂ comprises downwardly a bottom opening having a width equal to the dome opening 26 or wider than said dome opening. When the second dome 20 ₂ is secured above the first dome 20 ₁, the bottom opening comes substantially into coincidence with the dome opening 26, and the second volume is in communication with the first volume via said dome opening 26 (and reciprocally). The hydrocarbon fluid that exits from the leaking device 2 is going naturally upwardly from the first volume to the second volume via said dome opening 26.

The first and second domes 20 ₁, 20 ₂ may comprise fastening means so as the second dome 20 ₂ is automatically secured to the first dome 20 ₁ as soon as the second dome is set down on the first dome. Any known mechanical means can be used for said fastening means, such as pins, spring loaded pins, etc . . . The fastening means are locked automatically by the setting down of the second dome above the first dome. They might be unlocked manually or remotely or via any actuation mean.

The containment system 1 can be composed of a plurality of modules, each one being installed above the other. The modules are preferably automatically secured one to the other by fastening means that automatically lock themselves when a second module is set down above a first module.

The upper portion of the second dome 20 ₂ comprises the upper output opening 22 of the dome 20 and is adapted to be connected to a pipe 50 for extracting the hydrocarbon fluid from the containment system 1 to a recovery boat 6 at the sea surface 4, so as the hydrocarbon fluid is recovered.

In a vertical plane (XZ), the upper portion 24 of the first dome 20 ₁ may have a convergent shape from the lateral portion 25 up to the dome opening 26. The dome 20 is a cover that can have advantageously an inverted funnel shape.

The hollow structure of the dome 20 (first and second domes 20 ₁, 20 ₂) forms a largely opened cavity 21 in the direction to the seafloor. It is positioned above and around the leaking device 2 so as to accumulate the light hydrocarbon fluid.

The cavity 21 accumulates hydrocarbon fluid coming upwardly from the leaking device 2, i.e. oil and/or natural gas. The hydrocarbon fluid fills the upper volume of the cavity, down to an interface level IL.

According to a first variant, the anti hydrates system 30 is an injection system that injects an injection fluid IF into the cavity 21. The injection system 30 may inject the injection fluid inside the first volume of the first dome 20 ₁ and/or the second volume of the second dome 20 ₂.

The injection system inputs injection fluid having a chemical effect on the fluids inside the cavity to actively avoid hydrates formation or hydrates agglomeration that may increase fluid viscosity in forming a slurry fluid.

The injection system 30 may comprise a plurality of output ports spread only inside the second volume (the volume of the second dome 20 ₂) so as to ensure a treatment of the hydrocarbon inside said second volume. Hydrates formation is then prevented inside the second volume. Then, the containment system cannot be clogged. And, the hydrocarbon fluid can be extracted via the upper output opening 22 of the second dome 20 ₂.

The injection system 30 may injects injection fluid IF from the upper portion, the lateral portion or from both portions of the second dome 20 ₂.

The injection system 30 may comprise a plurality of output ports spread near or at the dome opening 26.

The injection fluid IF may be sea water pumped near the sea surface 4 via a pump 63. The pumped sea water may be used as it, i.e. at the temperature of sea water at the sea surface 4, or heated by additional means.

The injection fluid may be water, salted water, sea water, oil, gas oil, dead oil, or crude oil.

The injection fluid may be an alcohol, an ethanol, a methanol, a glycol, an ethylene glycol, a diethylene glycol, or a low-dosage hydrate inhibitor (LDHI).

The injection fluid may be additionally heated by a fluid heater or not, for preventing to form hydrates. In case of use water, the injection fluid is preferably heated. The fluid heater may by on a vessel at sea surface, or integrated in the injection system itself, or integrated in the second dome 20 ₂. The injection system 30 preferably injects the injection fluid at a velocity that is low, and preferably at a velocity that is lower than 0.5 meter per seconds. The injection fluid is better mixed to the fluid inside the cavity, and preferably better mixer to the fluid inside the second volume of the second dome 20 ₂.

According to a second variant, the anti hydrates system 30 is a heating system that heats at least a portion of the cavity for actively preventing or remediating hydrates formation inside the cavity and/or for preventing adhesion of hydrates on an inner surface of the first and/or second dome.

The heating device inputs heat energy having a thermal effect to actively avoid hydrates formation and/or hydrates adhesion.

The heating system is for example a fluid circuit fed with a heated or hot fluid, or a resistive electric circuit. The heating system is for example situated in or on the second dome 20 ₂. The second dome 20 ₂ and/or the second volume of the second dome and/or a portion of the second volume is heated. For example, only a boundary layer above the inner surface is heated. The boundary layer is eventually less than 10 mm thick, and for example less than 5 mm thick. Thanks to the heated boundary layer, hydrates do not adhere to the inner surface of the second dome 20 ₂ and can be extracted from the cavity via the flow of hydrocarbon fluid.

The term “heated” means having a temperature increase enough to obtain the anti hydrates effect (no formation or no adhesion). For example, the temperature may be increased of at least 10° C., and preferably between 10° C. and 15° C. above a hydrate formation temperature. The hydrate formation temperature is determined by hydrocarbon fluid and the pressure near the leaking device 2 (i.e. the depth). Temperature-pressure curves for every hydrocarbon fluid are known, these curves identifying the phase changes, and more particularly conditions for hydrates formation.

The fluid inside the second dome 20 ₂ is prevented of hydrates formation and/or hydrates adhesion on inner surface. The hydrocarbon fluid accumulated inside said second dome can be extracted via the upper output opening.

The fluid inside the first dome 20 ₁ is itself prevented of hydrates formation by the heat from the hydrocarbon fluid itself, and filling a great portion of the first volume inside the first dome 20 ₁.

In all the variants, the containment system 1 advantageously comprises at least one level sensor 60 for measuring the interface level IL of the fluid interface between sea water and the hydrocarbon fluid inside the dome 20.

The level sensor 60 may give a first measurement of a liquid level corresponding to the interface level IL between the liquid component of the hydrocarbon fluid (e.g. oil) and the sea water, and a second measurement of a gas level corresponding to an interface between the liquid component and a gas component (e.g. natural gas) of the hydrocarbon fluid.

The containment system 1 may also comprise a temperature sensor 70 for measuring a temperature of the fluid inside cavity 21. The temperature sensor 70 may provide a local temperature value, a mean temperature value of a plurality of locations inside the cavity, or a plurality of temperature values inside the cavity.

The containment system 1 may also comprise a pressure sensor for measuring a pressure of the fluid inside cavity 21.

The containment system 1 additionally comprises an output valve 62 connected to the upper output opening 22 and/or pipe 50 for outputting the recovered hydrocarbon fluid to the recovery boat 6. The output valve 62 is located in a vessel (as illustrated on FIG. 1) or just above the dome 20 or integrated in the dome at the upper output opening 22 (as illustrated on FIG. 2).

Then, a user or a control unit 61 determines or calculates a control value on the bases of a measured value of the interface level IL and/or the temperature inside the cavity and/or a pressure value, and operates the output valve on the bases of the control value for outputting hydrocarbon fluid from the cavity. The user or the control unit 61 may determine the control value to keep the interface level at a constant level inside the cavity 21.

The containment system 1 may also comprise a exhaust output valve 64 for example situated above the dome 20 near the upper output opening 22. The exhaust output valve 64 is adapted for opening and/or closing the cavity to the sea environment.

The sea output valve 64 is advantageously operated on the bases of an exhaust control value that is opposite to the control value of the output valve 62: the output valve 62 is closed when the exhaust output valve is opened, and the output valve 62 is opened when the exhaust output valve is closed.

The pipe 50 is advantageously a two concentric tubes pipe, having an inner pipe 51 forming an inner channel, and an outer tube 52 surrounding said inner pipe 51 and forming an annular channel between the inner tube and the outer tube. The inner channel may be connected to the upper output opening 22 and used to extract the hydrocarbon fluid from the cavity 21. The annular channel may be therefore connected to the injection system 30, and used to feed it with the injection fluid from the surface. However, it is apparent that the two channel of such pipe can be connected to the dome according to the other inverse possibility without any change.

The containment system 1 may also comprise independent pipes: A first pipe 51 connected to the upper output opening 22 and used to extract the hydrocarbon fluid from the cavity 21, and a second pipe 52 connected to the injection system 30 and used to feed it with the injection fluid from the surface.

The containment system 1 may comprise other output openings and/or pipes for feeding additionally fluids, or for extracting other fluids, liquid or gases from the cavity.

For example, the containment system 1 may comprise a drain valve for purging or limiting the quantity of water inside the cavity 21. Said drain valve might be positioned proximal to the base level BL (seafloor).

Advantageously, the cavity 21 can be used as a phase separator for separating the water and the hydrocarbon fluid, and for separating each phase of the hydrocarbon fluid (oil, gas) so as to extract them separately.

The above phase separation is preferably done inside the second volume of the second dome 20 ₂.

To this end, the dome 20 may comprise:

-   -   a first output opening for extracting a first phase from the         cavity, said first phase being for example an oil phase of the         hydrocarbon fluid, and     -   a second output opening for extracting a second phase from the         cavity , said second output opening being positioned on the dome         at a level proximal to a highest level of the dome, said second         phase being lighter than the first phase, and being for example         a gas phase of the hydrocarbon fluid.

Each output opening (first and second) is connected to a pipe: an oil pipe 51 b for extracting oil and a gas pipe 51 a for extracting gas.

Thanks to the above first and second output openings, quantities of each phase (oil, gas) can be limited inside the cavity 21 to predetermined values. An Archimedes force maximum that applies on the containment system 1 can be predetermined, and the weights of the foot 20 c can therefore be predetermined for maintaining the containment system 1 landed at the seafloor 5.

The first output opening is positioned at a predetermined level inside the dome. So as the phase separation works properly, an oil-gas interface must be above said predetermined level. The level sensor 60 may provide the level of said oil-gas interface.

Eventually, as illustrated on FIG. 4, the containment system 1 comprises a mixer device 80 that mixes the hydrocarbon fluid, and mixes the various phases and components of the hydrocarbon fluid. The mixed fluid is therefore more homogeneous, and more easily transferred or extracted via a pipe, as the flow of said mixed fluid is more constant and continuous.

The mixer device 80 is preferably outside the second dome 20 ₂ as illustrated on the figures.

Eventually the mixer device 80 is integrated inside the dome 20, and preferably integrated inside the second dome 20 ₂.

Eventually, the oil pipe 51 b and the gas pipe 51 a are connected to the mixer device 80, said mixer device 80 being located outside of the second dome 20 ₂. Then, the fluids from each pipe are mixed by the mixer device.

In both cases, thanks to the mixer device 80, only one pipe is needed to extract all the components of the hydrocarbon fluid from the seafloor to the sea surface. It is therefore less expensive and the installation is more rapidly installed above the leaking device 2.

The containment system 1 may comprise a plurality of outputs, each of them mixed with a quantity of gas from a gas output via a plurality of mixer devices.

Then, the above mixer device 80 can be used in any containment system: in a containment system having only one dome as illustrated on FIG. 5 and in prior patent applications of the applicant, i.e. patent applications PCT/EP2012/075675, PCT/EP2012/075676, PCT/EP2013/065359, PCT/EP2013/068644 herewith enclosed by reference.

According to a first variant illustrated on FIG. 4, the oil pipe 51 b is equipped with an oil valve 80 b to control the flow of oil fluid, and therefore the mix and its ratio.

According to a second variant illustrated on FIG. 5, the oil pipe 51 b is equipped with an oil valve 80 b, and the gas pipe 51 a is equipped with a gas valve 80 a. These valves are manually controlled or remotely controlled (via a Remotely Operated Vehicle) or automatically controlled via the control unit 61 (closed loop control), for example, on the bases of interface level measurements provided by a level sensor 60.

Moreover, the dome 20 may comprises thermal insulating material, so as to thermally insulate the cavity 21 from the cold environment of sea water. Ideally, the dome 20 may be manufactured with at least a thermally insulating material, said thermally insulating material preferably having a thermal conductivity lower than 0.1 W.m⁻¹.K⁻¹. The dome 20 may have an overall heat transfer coefficient lower than 2 W.m⁻².K⁻¹, and more preferably lower than 1 W.m⁻².K⁻¹ based on the overall internal dome wall surface.

The above insulating improvements may apply to all the dome (first and second dome), or the first dome only, or the second dome only, or a portion of them.

The first dome 20 ₁ is however preferably thermally insulated so as to keep its huge first volume to a highest temperature as possible, said first volume being heated by the heat of the hydrocarbon fluid outputting from the leaking device 2.

The following thermal insulating materials may be used: synthetic material such as Polyurethane (PU) or polystyrene material, or a fibre textile with Polyvinyl chloride (PVC) coating or PU coating, or Alcryn®. The thermal insulating material may be foam, or a gel contained inside a double wall structure.

The thermal insulation of the dome 20 passively insulates the cavity 21, while the injection system 30 actively insulates the cavity 21. Both effects prevent the formation of hydrates inside the cavity 21.

The cavity 21 is a volume storing a quantity of hydrocarbon fluid and absorbing the fluctuations of hydrocarbon fluid flows.

The dome 20 comprises an over pressure valve 23 that extract fluid out of the cavity and into the environment if a pressure difference between the cavity 21 and the environment exceeds a predetermined pressure limit.

The predetermined pressure limit is for example of 10 bars, 20 bars, or 50 bars. This limit has to be determined accordingly with the cavity size and the leaking device flow.

The over pressure valve is for example a ball check valve. The ball check valve comprises a support element, a ball, and a spring that loads the ball to the support element so as to close an opening. The tuning of the spring load is adapted to the predetermined pressure limit.

The cavity 21 is closed, and if hydrates formation is prevented, the fluid inside the cavity is rapidly heated by the hydrocarbon fluid itself outputting from the leaking device 2.

The over pressure valve 23 insures that the pressure inside the cavity is not increasing, and then insuring that the containment system is not destroyed.

The predetermined pressure limit may insure that hydrates formation is prevented.

FIG. 2 is a second embodiment of a containment system 1 according to the invention. This containment system 1 is similar to the first embodiment. It comprises the same elements as the first embodiment, and can have the same variants as disclosed above. The second embodiment of the containment system 1 differs in that:

-   -   the first dome 20 ₁ comprises a lower output opening 23 that is         situated on the lateral portion 25 of the dome so as the first         dome is opened to the sea at a low level DL near the seafloor,         and     -   it further comprises a wall 10 inside the first dome 20 ₁.

The wall 10 extends from a lower end 10 a at the base level to an upper end 10 b at a first level L1, said wall 10 being substantially sealed to the seafloor around the leaking device 2.

The wall 10 and the dome 20 are preferably independent parts or members, each of them installed at the seafloor independently from the other, and each of them being fixed preferably to the seafloor. The wall 10 is installed on the seafloor before the dome 20, so as to cancel the convection of cold sea water before the installation of the dome 20.

For example, the wall 10 comprises foot 10 c having heavy weights for sealing and securing the wall 10 to the seafloor. The dome 20 may have similarly foot 20 c for securing it to the seafloor.

The wall 10 completely surrounds the leaking device 2. In a horizontal plane (XY), the wall 10 has a closed loop shape encompassing the leaking device 2. Said shape may be for example a circle shape, a square shape or any polygonal shape.

The wall 10 has an outer diameter D10. This outer diameter corresponds to a maximum distance between two external points of the wall, taken in an horizontal plane at a level near the first level L1. The outer diameter D10 is for example of 6 meters or more.

The wall 10 then extends upwardly from a lower end 10 a at the base level BL to an upper end 10 b at the first level L1. The first level L1 is preferably higher than a total height of the leaking device 2.

The wall 10 defines an inner wall volume 11. This volume 11 is substantially isolated (not in direct communication) with the environment sea water, according to a horizontal direction (XY). The volume 11 is opened upwardly, according to a vertical direction (Z). Such wall 10 cancels any horizontal flow of sea water that is usually sucked by the flow of hydrocarbon fluid outputting from the leaking device 2. This dramatically reduces the thermal convection exchange between the cold sea water and the hydrocarbon fluid. This first effect cancels the hydrate formation.

The first level L1 is preferably at least twice the total height of the leaking device 2, and more preferably three times higher than it. The wall 10 can cancel efficiently the convection effect of cold sea water.

FIGS. 3a to 3e are an exemplary of a containment system according to the schematic of FIG. 1 and also showing a method for using or installing said containment system.

In this exemplary, the dome 20 is composed of a base tubular structure represented on FIG. 3a , said base tubular structure comprising the foot 20 c for securing the dome to the seafloor, and a tubular structure extending upwardly from the lower end 25 b (attached to said foot 20 c) to the upper end 25 a and extending in a radial direction from said upper end 25 a.

The tubular structure is a rigid frame giving a general shape to the first dome 20 ₁. But, it does not close the volume of the cavity 21.

The tubular structure supports a first cover 27 for covering laterally said tubular structure and forming the lateral portion of the first dome 20 ₁. The first cover 27 is a cylindrical tube that covers and closes the lateral portion 25 of the first dome 20 ₁. The first cover shape is adapted to the lateral shape of the tubular structure. The first cover is attached to (secured to) said tubular structure by any securing means.

The tubular structure also supports a second cover 28 for covering upwardly the tubular structure and forming the upper portion of the first dome 20 ₁. The second cover 28 is an annular part, having a lower ring 28 a that fits to the upper end 25 a of the first cover 27, a intermediate ring 28 b having an annular and conical shape extending from said lower ring 28 a, and an upper ring 28 c extending from the centre of the intermediate ring. The upper ring 28 c is a cylindrical tube that keeps the dome opening 26 opened and that is adapted for receiving the second dome 20 ₂. The second cover shape is adapted to the upper shape of the tubular structure. The second cover is attached to (secured to) said tubular structure by any securing means.

The fist and/or second covers 27, 28 may be rigid elements, for example made of welded metal sheets.

The first and/or second covers 27, 28 may be flexible elements, for example made of textile. They may be extendable, or deployable, or telescopic from a retracted position to a deployed position that covers the surface of the lateral portion 25 or upper portion 24 of the first dome 20 ₁.

The second dome 20 ₂ is a smaller, and may be a rigid box adapted to be attached above the upper ring 28 c of the second cover 28.

The method for using or installing the containment system 1 according to the invention is now explained with the FIGS. 3a to 3 e.

At FIG. 3a , a base tubular structure is landed and sealed around the leaking device 2, said leaking device being substantially situated at the centre of the base tubular structure (according to a horizontal XY direction). The leaking device 2 is completely inside the volume of the base tubular structure, said volume being the first volume of the first dome 20 ₁.

At FIG. 3b , the first cover 27 is mounted on and secured to the base tubular structure so as to close the lateral portion 25 of the dome.

At FIG. 3c , the second cover 28 is mounted on and secured to the base tubular structure and above the first cover 27 so as to close the upper portion of the dome 24, a dome opening 26 being kept opened.

At FIG. 3d , the second dome 202 is moved downwardly towards the first dome 20 a.

During this step, the injection system 30 may inject the injection fluid IF into the second volume of the second dome 20 ₂. This second volume is rapidly filled with the injection fluid. Hydrates formation is then prevented inside this second volume. The quantity of injection fluid needed to fill said second volume is much smaller than the one that would be necessary to fill the first volume or to prevent hydrates formation inside a dome having the first volume.

At FIG. 3e , the second dome 20 ₂ is secured to the first dome 20 ₁.

Therefore, the containment system 1 according to the invention comprises:

-   -   a dome 20 forming a cavity 21 under said dome to accumulate         hydrocarbon fluid coming upwardly from the leaking device, said         dome comprising at least one upper output opening 22 adapted to         extract the hydrocarbon fluid for recovering, and     -   an injection system 30 that inputs an injection fluid IF into         the cavity for preventing or remediating hydrates inside the         cavity.

The dome 20 further comprises a first dome 20 ₁ having a first volume, and a second dome 20 ₂ having a second volume smaller than the first volume, the second dome 20 ₂ being situated upper the first dome 20 ₁.

The method according to the invention for using or installing the containment system 1 comprises the following successive steps:

-   -   a) installing the first dome (20 ₁) on the seafloor around the         leaking device, the cavity completely surrounding and including         the leaking device,     -   b) installing the second dome (20 ₂) upper the first dome (20 ₁)         so as the first and second volumes are in communication via a         dome opening (26).

Thanks to the above method, the volume the quantity of needed injection fluid to prevent hydrates formation is smaller. The flow of this injection fluid is highly reduced.

The time delay for installing the second dome 20 ₂ above the first dome 20 ₁ is shorter than the time delay for installing the first dome on the seafloor. The risk of hydrates formation is then reduced.

The injection system 30 preferably injects the injection fluid IF into the second volume of the second dome 20 ₂ before the second dome is installed upper the first dome 20 ₁.

Preferably, the second volume is completely filled with injection fluid before said installation of the second dome.

Additionally, the containment system 1 further comprises a sensor 60 and an output valve 62 connected to the upper output opening 22. In the method, we are:

-   -   c) measuring by the sensor 60 an interface level IL of a fluid         interface between hydrocarbon fluid and any other fluid inside         the dome, and     -   d) controlling the output valve 62 on the bases of the interface         level IL measured by the sensor 60 for outputting hydrocarbon         fluid from the cavity 21.

The quantity of hydrocarbon fluid can be kept high. This fluid is relatively hot, and hydrates formation is prevented.

The output valve 62 is controlled so as to keep the interface level IL lower or equal to a level LL of output of the hydrocarbon fluid from the leaking device.

The jet of hydrocarbon fluid from the leaking device 2 is directly entering the hydrocarbon fluid accumulated inside the dome. The hydrocarbon fluid is relatively hot, and cold water mixture is also prevented. Hydrates formation is therefore prevented.

The embodiments above are intended to be illustrative and not limiting. Additional embodiments may be within the claims. Although the present invention has been described with reference to particular embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.

Various modifications to the invention may be apparent to one of skill in the art upon reading this disclosure. For example, persons of ordinary skill in the relevant art will recognize that the various features described for the different embodiments of the invention can be suitably combined, un-combined, and re-combined with other features, alone, or in different combinations, within the spirit of the invention. Likewise, the various features described above should all be regarded as example embodiments, rather than limitations to the scope or spirit of the invention. Therefore, the above is not contemplated to limit the scope of the present invention. 

1. A containment system for recovering hydrocarbon fluid from a leaking device that is situated at the seafloor and that is leaking hydrocarbon fluid from a well, wherein the containment system is adapted to be landed at the seafloor corresponding to a base level of the containment system, and wherein the containment system comprises: dome intended to be secured to the seafloor around the leaking device and forming a cavity, said cavity being adapted to completely surround and include the leaking device, and to accumulate hydrocarbon fluid coming upwardly from the leaking device, said dome comprising at least one tipper output opening adapted to extract the hydrocarbon fluid for recovering, and an anti hydrates system that actively prevents or remediates hydrates inside the cavity, and wherein the dome comprises a first dome having a first volume adapted to receive the leaking device, and a second dome having a second volume smaller than the first volume, the second dome being situated above the first dome, and the first and second volumes being in communication via a dome opening.
 2. The containment system according to claim 1, wherein the second volume is smaller than a ¼^(th) of the first volume, and preferably smaller than a 1/10^(th) of the first volume.
 3. The containment system according to claim 1, wherein the second volume is higher than a 1/20^(th) of the first volume.
 4. The containment system according to claim 1, wherein the dome opening is between 2 and 4 meters wide.
 5. The containment system according to claim 1, wherein the first dome is thermally insulated with an insulating material for having an overall heat transfer coefficient of the first dome lower than 1 W.m⁻².K⁻¹.
 6. The containment system according to claim 1, wherein the anti hydrates system is situated into or onto the second dome.
 7. The containment system according to claim 1, wherein the anti hydrates system is a heating system for heating at least a portion of the cavity.
 8. The containment system according to claim 1, wherein the anti hydrates system is an injection systems that inputs an injection fluid into the cavity.
 9. The containment system according to claim 8, wherein the injection system comprises a plurality of output ports spread inside the second volume or at the dome opening, said output ports being fed with the injection fluid.
 10. The containment system according to claim 8, further comprising a fluid heater for heating the injection fluid before injection into the cavity.
 11. The containment system according to claim 8, wherein the injection fluid comprises one or a combination of the fluid components chosen in the list of water, salted water, dead oil, an alcohol, an ethanol, a methanol, a glycol, an ethylene glycol, a diethylene glycol, and a low-dosage hydrate inhibitor.
 12. The containment system according to claim 8, further comprising a pipe having an inner tube forming an inner channel, and an outer tube surrounding said inner tube and forming an annular channel, and wherein the inner channel is used to extract the hydrocarbon fluid from the upper output opening and the annular channel is used to feed the injection system with at least an injection fluid, or inversely.
 13. A method for using a containment system for recovering hydrocarbon fluid from as leaking device that is situated at the sea floor and that is leaking hydrocarbon fluid from a well, and wherein the containment system comprises: as dome forming a cavity under said dome to accumulate hydrocarbon fluid coming upwardly from the leaking device, said dome comprising at least one upper output opening adapted to extract the hydrocarbon fluid for recovering, and an anti hydrates system that actively prevents or remediates hydrates inside the cavity, and wherein the dome comprises a first dome having a first volume, and a second dome having a second volume smaller than the first volume, the second dome being situated upper the first dome, and wherein the method comprises the following successive steps: a) installing the first dome on the seafloor around the leaking device, the cavity completely surrounding and including the leaking device, b) installing the second dome upper to the first dome so as the first and second volumes are in communication via a dome opening.
 14. The method according to claim 13, wherein the anti hydrates system is a heating system for heating at least a portion of the cavity.
 15. The method according to claim 13, wherein the anti hydrates system is an injection systems that inputs an injection fluid into the cavity.
 16. The method accordion to claim 15, wherein the injection system injects the injection fluid into the second volume of the second dome before step b).
 17. The method according to claim 15, wherein the injection system injects the injection fluid at a velocity that is low, and preferably at a velocity that is lower than 0.5 meter per seconds.
 18. The method according to claim 13, wherein the containment system further comprises a level sensor and an output valve connected to the upper output opening, and wherein the method further comprises the following steps: c) measuring by the level sensor an interface level of a fluid interface between hydrocarbon fluid and any other fluid inside the dome, d) controlling the output valve on the bases of the interface level measured by the level sensor for outputting hydrocarbon fluid from the cavity.
 19. The method according to claim 18, wherein at step d), the output valve is controlled so as to keep the interface level lower or equal to a level of output of the hydrocarbon fluid from the leaking device.
 20. The method according to claim 13, wherein the containment system further comprises a temperature sensor and an output valve connected to the upper output opening, and wherein the method further comprises the following steps: c) measuring by the temperature sensor a temperature of the fluid inside the dome, d) controlling the output valve on the bases of the temperature measured by the temperature sensor for outputting hydrocarbon fluid from the cavity. 